1. Field of the Invention
This invention relates to a white balance processing device which is advantageously adapted for a solid-state camera or the like.
2. Description of the Related Art
Heretofore, the device of the above-stated kind has been arranged as shown in FIG. 5 of the accompanying drawings. Referring to FIG. 5, correlative double sampling (abbreviated to CDS) circuits 21 are provided for removing noises such as 1/f and reset noises that are included in a video signal output from an area sensor or the like. Voltage changeable amplifier (abbreviated to VCA) circuits 22 and 24 are arranged to have their amplification degree variable by changing their voltage values. An amplifier circuit 23 is arranged to have its amplification degree unvarying. Clamp circuits 25 are arranged to perform a clamping process on the video signal. Analog-to-digital (abbreviated to A-D) converters 26 are arranged to convert an analog video signal into a digital video signal. A white balance control circuit 27 is arranged to generate a control voltage for changing the amplification degrees of the VCA circuits 22 and 24 for white balance control.
The white balance control is performed in the following manner: R (red), G (green) and B (blue) video signals which have been processed by the CDS circuits 21 are supplied to the amplifier circuits 22, 23 and 24 respectively. The G video signal is amplified to a given amplification degree and output from the amplifier circuit 23. Meanwhile, the R and B video signals are amplified by the VCA circuits 22 and 24 to amplification degrees which are controlled by the control signals RWB and BWB output from the white balance control circuit 27 in such a way as to be at a level equal to the output level of the G video signal in respect of a white object. In other words, the white balance control is performed to cause the R, G and B video signals output from the amplifier circuits 22, 23 and 24 to be at the same level for a white object.
However, since the conventional device has been arranged to control the white balance by using the voltage changeable amplifiers as described above, the variable range of their amplification degrees is relatively narrow. Besides, a waveform distortion results from deterioration of phase and frequency characteristics.